Such matting has in the past been used as soil erosion protection, especially below water level, for river shipping lanes and canals. The gripper layer reaches through the fine particles deposited on said soil and forms an interlocking bond with the substructure. The gripping layer of this known matting, which is described in e.g. "Neue Landschaft" 3/77, p. 116 righthand side, penultimate paragraph, or in the borchure 7393/7/10 of Oltmanns Ziegel and Kunstoffe Co. 2905 Edewecht/Jeddeloh I, is fused at certain points to the filter layer, which may in turn consist of a number of fiber webs and/or woven fabric layers interlocked by needle-punching.
Although literature claims that the use of such matting prevents particle rearrangement under the filter matting, practice indicates that especially in the presence of fine soil particles (class 4) rearrangement or displacement of the particles cannot be entirely avoided, i.e. the filter cake is subjected to washing of the finest particles due to erosion.
An object of the invention is to prevent grain rearrangement and thus against washing of the filter cake. Another object is to increase the peel strength of the matting, i.e., the resistance to separation of the gripper layer from the filter layer.